I have set up a zimbra and configured outlook as the mail clients.

I configured my account on outlook on a computer running on the LAN. I then changed the logon information(password) on outlook.

When I open outlook, It asks me for the password. When I click cancel, I can still send mail from the configured account

Does this mean that my zimbra server is an open relay on the LAN? If so, How do I stop this?

I am using port 25 as the "outgoing server".